10179096_2103 S. GRAND - Plan (2)

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Former Circuit One 2103 S. Grand Avenue. Santa Ana. California Proiect No. 11-0106 "May and June 2012 Site Assessment Report" did not include an assessment of completed exposure pathways for copper which is known to be present as a soil contaminant at the Site. During a meeting with the CRWQB on October 9, 2012, the CRWQCB suggested collecting additional soil samples beneath the area where copper was found above its STLC. RS requested to obtain groundwater samples from wells MW-5 and P-6B and test the groundwater for copper in lieu of collecting soil samples to determine if there is groundwater contamination by copper in the study area. The CRWQB agreed to this suggestion. The wells were sampled on October 30, 2012 (RS 2012D). Copper was not detected above its minimum detection limit (MDL) in the groundwater samples collected from wells MW-5 and P- 68. Well P-68 is located near the former clarifier in Suite 2103 S. Grand Avenue. Well MW-5 is located downgradient of the former clarifier just outside the suite. RS has shown that there is some soil at the site with copper that exceeds its STLC. This RAP is prepared to describe the remediation of the soil with copper above its STLC. It is known that there is some copper in the soil at depths of 3 and 5 feet bgs in the vicinity of the former clarifier above what is believed to be its background concentration of between 19 mg/kg and 43 mg/kg. But the copper concentration in the soil is below 10 times its STLC which means it does not have a leaching potential. Copper was not found above its reporting limit in the groundwater samples collected in October 2012 by RS from wells P-6B and MW-5 and the groundwater samples collected in 1993 from wells MW-1, MW-3, P-2, P-5, MW-5 and MW-2 by GRI. This indicates that the copper exposure to groundwater on the site conceptual model is incomplete. RS does not believe that there is any threat to groundwater contamination by copper after the soil with copper STLC of 25 mg/L or higher is removed. The soil that exceeds copper STLC equal or above 25 mg/L are shown on Figures 5 and 6. 3.0 OBJECTIVES AND TECHNICAL APPROACH The objective of the remediation is to minimize the presence of copper that is in soil above its STLC. The soil with copper concentration above its STLC should be remediated to prevent its leaching into the groundwater and contaminating it. The most cost effective remediation method is by excavation and offsite disposal of the contaminated soil. The cleanup goal for copper impacted soil is its STLC which is 25 mg/L. The vertical extent of copper impacted soil that requires removal is between 2 and 3 feet bgs. 4.0 SCOPE OF WORK The following sections describe the scope of work for the remedial excavation: 4.1 Prefield Activities This task will consist of activities to be performed in preparation for fieldwork. Prefield activities to be conducted as part of this task include: • Prepare and submit this soil RAP to the CRWQCB for their review and approval • Update the site health and safety plan • Obtain appropriate permit • Screen subsurface for underground utilities • Notify underground service alert regarding excavation • Schedule subcontractor to perform the remedial excavation REMEDIATION SCIENCES 5 .